Printed retroreflective sheet

ABSTRACT

A method of printing a sign including the steps of providing a sign component and an image definition, applying dry toner powder to surface portions corresponding to the image definition, and fusing the applied toner. The image definition is provided as an embossed pattern. A toner composition and a computer program for printing are also disclosed. &lt;IMAGE&gt;

A microfiche appendix is included in this application showing certaincomputer software. The appendix comprises one microfiche with 73 frames.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND OF THE INVENTION

The present invention relates to the production of signs, and inparticular, to the printing of an image for a weather resistant signsuch as a license plate.

Vehicle license plates are a challenging problem. They must provide anoverall similarity of styling or appearance to enable rapid recognitionof license plates issued by various licensing authorities and to inhibitcounterfeiting. At the same time, license plates need to provide adistinct, individualized, and unique identifier code or image for eachvehicle. In essence, each vehicle requires a custom, short runmanufacturing process to incorporate its unique code or image upon acommonly styled license plate blank.

The best known manufacturing process for incorporating the unique imagehas been stamping or embossing a metallic plate to first provide raisedletters or numbers on a plate. Subsequently, the raised letters ornumbers are contacted by a liquid ink or paint carried upon a roller orpad. The liquid ink or paint dries to provide a contrasting image whichcorresponds to the embossed image or raised pattern of the plate. Inorder to improve the weather resistance, after drying of the ink, theplate is dipped in a liquid clear coating agent (i.e. a solvent bornresin or plastic). The resulting plate is relatively durable. However,the embossing and inking process is labor intensive. In the U.S. most ofthe labor for this process has been prison labor. In other areas of theworld, however, private industry or governmental employees are the laborsources for license plate manufacture.

In recent years, many licensing authorities have offered "vanity"license plates at a premium license fee. Such plates allow the licenseeto participate in the selection of an attractive or meaningful printeddesign to be entered upon their license plates. Unfortunately, theproduction of such "vanity" license plates also entails a significantlygreater production cost. Additionally, some licensing authorities desireto reuse previously abandoned identifying codes or images. Preparationof license plates for such nonsequential images also represents a custommanufacturing operation, similar to that required for "vanity" plates. Amore versatile and efficient printing process would be useful forpreparing regular, nonsequential, and vanity license plates.

Another aspect of the present embossing and liquid inking process is therelease of solvent vapor from the drying ink. This solvent release is inaddition to solvent released by the dipping and subsequent drying of theprotective clear coating layer. The manufacture of large quantities oflicense plates requires substantial investment in drying ovens andsolvent vapor ventilation. Increased scrutiny of possible environmentaland health risks associated with various solvent vapors appears to be atrend throughout the world. It would be advantageous to eliminate thegeneration of solvent vapors from the process of printing licenseplates.

Many traffic signs and license plates have a retroreflective propertywhich is generally considered desirable in the industry. In such cases,inks or paints have been selected for compatibility with theretroreflective materials. A more versatile and efficient printingprocess would accommodate a variety of colorants and be compatible withretroreflective components used in license plates and traffic signs.

SUMMARY OF THE INVENTION

The present invention includes a method of printing a weather resistantsign when provided with a sign component having a surface to be printedand a definition of the image to be printed. Dry toner powder is appliedto portions of the surface corresponding to the image definition. Thetoner is fused to form a fused image upon the surface of the signcomponent. Preferably the surface, including the fused toner, is coveredby a protective coating to seal the fused toner within a weatherresistant package. The sign component to be printed may be an opaque orretroreflective sheet or, alternatively, a light transmitting(preferably transparent) cover film for use over an opaque orretroreflective sheet. The image definition may be mechanical, such asby embossing, or digital, such as by a computer generated signal from astored image, an optically scanned image, an image stored on microfilmor an image composed by a computer operator. The method may be practicedwithout the generation of solvent vapors and is also suitable for othershort runs of signs, such as street name signs.

The present invention also includes a license plate printed by themethod of this invention. A license plate of the present invention is alaminate including at least the following layers: a substrate, aretroreflective sheet layer upon the substrate oriented to provideretroreflection of light entering the retroreflective sheet oppositefrom the side laminated to the substrate, and a discontinuous imagelayer of fused toner over the retroreflective sheet. A preferred licenseplate of the present invention is a laminate including at least thefollowing layers: a substrate, a retroreflective sheet layer upon thesubstrate oriented to provide retroreflection of light entering theretroreflective sheet opposite from the side laminated to the substrate,a transparent protective top layer over the retroreflective sheet layer,and a discontinuous image layer of fused toner sandwiched between theretroreflective sheet layer and the transparent top layer. The licenseplates optionally may include an embossed image substantiallycorresponding to the fused toner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic of an embodiment of the present inventionemploying a mechanically defined image;

FIG. 2 is a schematic of an embodiment of the present inventionemploying a digitally defined image;

FIG. 3 is a schematic of another embodiment employing a digitallydefined image;

FIG. 4 is a partial cross section of a license plate of the presentinvention;

FIG. 5 is a diagram of the data flow within the preferred computerprogram of the present invention;

FIG. 6 is a process control flow chart for the preferred computerprogram of the present invention;

FIG. 7 is an illustration of the make character function of the program;

FIG. 8 is an illustration of the scan function of the program;

FIG. 9 is an illustration of the contrast function of the program;

FIG. 10 is an illustration of the make string function of the program;

FIG. 11 is an illustration of a portion of the scale function of theprogram;

FIG. 12 is an illustration of a second portion of the scale function ofthe program;

FIG. 13 is an illustration of the merge function of the program; and

FIG. 14 is an illustration of the print function of the program.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention includes a method of printing a weather resistantsign. The method includes the steps of providing a first sign componenthaving a surface, providing a definition of an image or graphic which isto be printed upon the surface of the first sign component, applying drytoner powder to portions of the surface which correspond to thedefinition of the image to be printed, and fusing the applied dry tonerpowder to form a fixed image upon the sign component surface. Thesesteps are explained in greater detail in the following detaileddescription of the preferred embodiments. Additionally, the inventionpreferably further includes the step of covering the surface and fusedtoner with a light-transmitting material to seal or sandwich the fusedtoner within a weather resistant package.

The invention will be explained with respect to the production of anautomotive license plate; however, the printing method is also suited tothe production of other signs and particularly to highway or outdoorsigns which are produced in very limited numbers. One particularlyappropriate sign to be printed by the method of the present invention isa street name sign.

In a first embodiment, a method for producing an embossed sign is shownschematically in FIG. 1. A sign component 22 is provided. Preferably,the sign component 22, is a thin piece of embossable material, forexample, a web 24 from a roll 26 of aluminum. A thickness of about 0.8mm is suitable for aluminum license plates. In a most preferredembodiment, the aluminum web may include a facing layer ofretroreflective sheeting. Such retroreflecting sheeting is known in thesign art. Enclosed lens retroreflective sheetings and the use of glassbeads to provide for reflexed light reflectors are described inPalmquist, et al., U.S. Pat. No. 2,407,680; May, U.S. Pat. No.4,626,127; Tung et al., U.S. Pat. No. 4,367,920; Tung et al., U.S. Pat.No. 4,511,210; and Tung et al. U.S. Pat. No. 4,569,920; Bailey et al.,U.S. Pat. No. 4,767,659; Bailey et al. U.S. Pat. No. 4,664,966; andBailey, U.S. Pat. No. 4,648,932; the disclosures of which areincorporated by reference herein.

Generally, enclosed lens retroreflective sheetings include, in order, anadhesive layer for application to a support such as a license plateblank, a specular reflective surface, a light transmitting spacinglayer, and a monolayer of glass beads within a light transmitting resinlayer. Often, a protective outer layer or top layer is also present.Retroreflective sheeting typically functions in the following manner:Light from an external source, is transmitted to the beads, which serveas lenses and direct the light toward the specular reflective surface,through the spacing. The reflective surface, preferably cupped abouteach of the glass beads, returns the light to the glass beads which inturn return the light toward the source.

The sign component 22 is embossed in an embossing unit 28. Embossingunits are well known in the production of license plates and typicallyinclude a male 30 and female 32 embossing molds or dies. When theembossing dies 30 and 32 are pressed together with the sign componentinterposed, a raised portion 34 is formed upon the sign component 22.These die pairs are interchangeable members of a set of dies andgenerally allow alphanumeric designs or images to be defined. Typically,the raised or embossed portion 34 protrudes about 0.15-0.20 cm relativeto the unaltered portions of the surface. If a retroreflective sheetingelement is included upon the sign component 22, the retroreflectivesheeting would be on the face of the sign component, overlying theraised portion 34 and arranged to provide a retroreflection property tothe surface to be printed.

Next, a printer unit 36 applies a dry toner powder to the raised portion34. Sign component 22 may be heated to facilitate transfer of toner. Theprinter 36 is configured so as to avoid application of the dry tonerpowder to the unraised portion of the sign component 22. An appropriateapplication system within the printer unit 36 includes a rotating drum38 carrying a layer 40 of dry toner powder. The rotating drum 38contacts or nearly contacts the raised portion 34 of the sign component22. The contact or near contact between the rotating drum 38 and theraised portion 34 allows a transfer of at least a portion of the layer40 of dry toner powder onto the raised portion 34, without transferringdry toner onto the unaltered portions (i.e. portions not embossed or inrelief) of the surface 35 of the sign component 22. The transfer of drytoner powder may be facilitated by warming of the embossed signcomponent 22. In the first embodiment, when the drum 38 is not anelectrostatic drum, a charge carrier is unnecessary in the dry tonerpowder. For example, a hard rubber roller adequately carries tonerpowder for transfer to embossed portions of a license plate blank.

Next, the applied dry toner powder 42 upon the raised portion 34 isfused. The fusing step may be by means of infrared heating 44 or othersuitable means of supplying an amount of heat sufficient to raise thetemperature of the dry toner powder to melt a binder component withinthe dry toner powder. Fusing serves to fix the image on the raisedportions. The resulting product may now be cut and used as a licenseplate or a sign at cutter 60.

Preferably, the fused dry toner is covered to protect it fromweathering. One method of covering is the well known "dip coating"method currently employed for covering license plates. An alternativemeans of covering is the lamination of a protective film which may besupplied in roll form. The web of protective film is brought into closeproximity to the surface and raised portions of the sign component, forexample, by a guide roller. A set of pinch rollers provide a nip forpressing the protective film over the raised portions 34 having fusedtoner and also onto unraised surface 35. The application of theprotective film seals the fused toner between the sign component 22(optionally having a retroreflective sheet on its face) and protectivefilm. Lamination of a protective film coat, such as an orientedpolyalkylmethacrylate coated with a thin layer of pressure-sensitiveacrylate adhesive, may also be employed as a combination fusing andcovering step. Appropriate temperatures serve to both fuse and laminatebut are less than temperatures which alter the orientation of the coverfilm.

The embossing unit 28 in the first method 20 serves to define a raisedimage upon the sign component 22. Traditionally, matching male 30 andfemale 32 dies must be employed to provide a particular definition of animage. In the schematic of FIG. 1, such a defined image is representedby the raised portion 34. Because license plates are prepared inextremely small groups (i.e. one or two plates per vehicle) and requiredistinct images for each vehicle, a change is required in the embossingunit 28 after every one or alternatively two license plates has beenembossed. The first method has the feature that a license plate may beprepared without the generation of any solvent vapors. The method couldbe substituted in the traditional manufacture of license plates. Such asubstitution, however, would not eliminate the production of a solventvapor from the clear dipping process.

Protective films which may have acceptable amounts of stretch orelongation have been disclosed in Bailey et al. U.S. Pat. No. 4,664,966and U.S. Pat. No. 4,767,659, the disclosures of which are incorporatedby reference herein. The method of the first embodiment is also suitablefor printing on an embossed sign lacking retroreflective sheeting.License plates with retroreflective sheeting, however, are particularlydesired by the industry.

In another embodiment, a method 100 of printing a license plateindependent of an embossing requirement is schematically shown in FIG.2. In the method 100, a retroreflective sheeting 102 is provided as aroll 104, and a web 106. The web 106 contacts or nearly contacts arotating drum 108. The surface 110 of the drum 108 is a reusable surfacewhich is initially electrostatically charged. The electrostatic chargingis altered by a laser imaging device 112 so as to form a latent imageand to allow acceptance of dry toner powder from a reservoir 114. Therotating drum reusable surface 110 carries portions of dry toner powder116 in an arrangement or pattern corresponding to a desired imagedefinition transferred to the reusable surface 110 by means of the laserimaging device 112. The dry toner portions 116 carried upon the reusablesurface 110 of the rotating drum 108 are brought into contact with andtransferred to the retroreflective sheeting web 106, thereby applyingdry toner powder to portions of the surface of the web 106 correspondingto the definition of the desired image. (The reusable surface 110remains with drum 108 for use in transferring new images to subsequentportions of the web 106.)

The dry applied toner powder is next fused by the application of heat,for example, by a heating roller or infrared radiation. After the fusingoperation, the retroreflective sheeting web 106 carries fused toner 122on its surface as an image corresponding to the originally defined imagesupplied to the printer.

Next, the retroreflective sheeting is laminated to a web 124 of supportmaterial, for example, 0.8 mm thick aluminum, from a roll 126. Thissupport material is brought into close proximity to the retroreflectivesheeting web 106 by a roller 128 and laminated by a pair of rollers 130and 132 forming a nip 134. Preferably, a protective transparent coversheet provided as a web 136 from a roll 138 is brought into closeproximity by a control roller 140 and is simultaneously laminated at thenip 134. As a final step, the license plate 142 is cut by a cuttingdevice 144.

Optionally, a rim embossing or debossing step may also occur subsequentto lamination at the nip 134. Such rim embossing or debossing serves tostiffen and further reinforce the resulting license plate 142. However,embossing or debossing is not required for printing by the method 100 ofthis embodiment.

In a preferred embodiment, the fusing of the toner powder occurssimultaneously with the lamination step, the appropriate temperaturebeing produced as part of the lamination step. In such an embodiment,the heat and temperature may be provided by heated rollers 130 and 132forming the nip 134.

A feature of the embodiment 100 is that license plates may be producedwithout the generation of any solvent vapors. In the past, solventvapors have typically been generated by the various solvent based inks,dies or paints used to produce an image. An additional feature of themethod 100 is that the image is defined electronically or digitally,rather than by mechanical definition as in the method 20 described inFIG. 1. The method 100, therefore, is particularly efficient inproviding short runs, such as, for example, one or two license plateimages, since male and female dies do not have to be changed or adjustedafter each extremely short run of license plates. Further, the range ofavailable images is not limited to those defined by a set of mechanicaldies, but rather is limited only to images which may be digitallydefined. Typically, a wider range of images can be defined digitallyrather than mechanically. Such digital images can also be changed fasterand with reduced labor.

In this and other embodiments of the present invention, reusable surface110 may be alternatively supplied by a belt surface or other well knownmeans for accepting a latent image, accepting dry toner powder accordingto the latent image, and subsequently transferring the dry toner powderto a surface to be printed.

In another embodiment of the present invention, another method 200 ofprinting an image without requiring embossing is schematically shown inFIG. 3. A web of a light transmitting protective sheet 202, preferablyprovided as a roll 204 has a surface 206 desired to be printed and to belaminated against a retroreflective sheet in the final product. Thesurface 206 contacts an electrostatic surface 208 of a rotating drum210. The surface 208 has been initially electrostatically charged. Thecharge is altered by a laser imaging apparatus 212, connected to adigital image definition mechanism (not shown). The laser 212 alters theelectrostatic charge on portions of the surface 208 such that imagingapparatus dry toner powder from a reservoir 216 is accepted by thesurface 208 in discrete areas corresponding to the image definition. Thediscrete portions 218 of dry toner corresponding to the imagedefinitions are next applied to the surface 206 of the protective coversheet 202 as it contacts the rotating drum 210. The thus applied drytoner powder adheres to the surface 206 in portions of the surface 206corresponding to the image definition provided by the digital imagedefinition mechanism. The applied dry toner powder 220 is next fused ina heating mechanism 222 to form a fixed image 224 borne upon the signcomponent surface 206.

Subsequently, a retroreflective sheeting web 226 provided by a roll 228is brought into close proximity to the surface 206 by a guide roller230. Preferably a support web, for example provided by a roll ofaluminum 234, is also brought into close proximity to the opposite sideof the retroreflective sheeting 226 by a roller 236. Next, a pair ofrollers 238 and 240 provide a nip 242 forcing the three webs into alamination. Subsequently, the resulting lamination may be cut intolicense plates 246 by a common cutter 244. Optionally and preferably,the rim of the license plate 246 may be rim embossed or rim debossedsubsequent to passage through the nip 242 to provide additional strengthto the license plate 246.

As in the method 100 of FIG. 2, the method 200 of FIG. 3 is free fromthe generation of solvent vapors and includes the feature of versatilityand efficient printing of short runs.

Also, as in method 100, the method 200 may alternatively and preferablycombine the fusing and lamination into a single simultaneous operationby the use of heated rollers 238 and 240 at the nip 242. Alternatively,a partial fusing step may be employed initially, to improve handling andreduce any tendency of smearing of dry toner, after application to theweb but prior to final fusing during lamination.

A preferred embodiment of a sign of the present invention is shown inexploded cross section in FIG. 4 at 300. The sign 300 includes anoptional top protective layer 302 having a first or outermost surface304 and a second or inner surface 306. The optional top protective layer302 is located on the side of the sign 300 which is to be viewed and ispreferably substantially transparent. Progressing through the sign 300from the viewing side, the next layer is the discontinuous image layer308, which is formed of fused dry toner powder. The image layer 308 hasa first or outwardly directed surface 310 and a second or inwardlydirected surface 312. Progressing through the sign 300, the next layeris a retroreflective sheet layer 314. In FIG. 4, the retroreflectivesheet layer 314 is shown as an enclosed lens type retroreflective sheetand is oriented to be retroreflective to light entering from thedirection of the optional top protective layer 302. Such sheets 314preferably include a lower adhesive layer 316, a specular reflectivelayer 318, a transparent spacer layer 324, a monolayer of lenses 320,and a transparent upper layer 322. Enclosed lens retroreflective sheetshave been previously described in Bailey et al. in U.S. Pat. No.4,664,966, incorporated by reference herein. Below the retroreflectivesheet 314 is a supporting substrate sheet 326, having an upper surface328 and a lower surface 330. A preferred substate is aluminum, however,steel, wood or plywood, or various plastic sheets may be suitablealternatives.

In finished form, the layers 302, 308, 314, and 326 of the sign 300 arelaminated together, such that light entering the sign 300 through thetop protective layer 302 and not encountering the discontinuous imagelayer 308 is retroreflected by the retroreflective sheet 314 to passback out though the top protective layer 302. Because the light isretroreflected, it generally returned along or near to its originalpathway. By comparison, light entering the sign 300 through the topprotective layer 302 and encountering the discontinuous image layer 308is affected differently. If the discontinuous image layer is opaque, itwill either absorb the light or reflect (but not retroreflect) the lightback through the top layer at generally a range of new angles. If thediscontinuous image is transmissive to some wavelengths of light andabsorptive to other wavelengths, the transmitted wavelengths will passthough to the retroreflective layer 314 for retroreflection back alongthe original pathway. When viewed, such light transmissive coloredimages 308 will provide a colored light image suitable for conveyinginformation to an observer.

Preferred solid toners have the following characteristics: resistance todegradation by weathering; and good adhesion to the substrate to whichthey are applied. A dry toner powder suitable for practicing the presentinvention requires a colorant and a binding agent. If the toner is to beapplied by an electrostatic drum surface, a charge carrier should alsobe included within the toner.

A suitable binding agent may be an alkyl substituted acrylate ormethacrylate polymer, with alkyl groups having from 1 to 9 carbon atoms,or mixtures of such acrylates, and especially a copolymer of methyl andbutyl methacrylates (such as for example, Acryloid B-66 available fromRohm & Haas Company). Other suitable binding agents are polyvinylacetals, for example, polyvinyl butryal (such as BUTVAR brand polyvinylbutryals B-90 or B-72 available from the Monsanto Chemical Company);polyolefins; polyesters (such as VITEL brand PE-200D from the GoodyearTire & Rubber Company or ARAKOTE 3000 brand carboxyl terminatedpolyester optionally in mixture with ARALDITE PT810 brand polyfunctionalepoxy resin (triglycidyl isocyanurate) both available from theCiba-Geigy Chemical Company); and vinyl resins (such as VINYLITE brandvinyl resin, VAGH copolymer of vinyl chloride and vinyl acetateavailable from the Union Carbide Corporation).

The preferred binding agents are characterized by relatively hightransparency and clarity. Additionally, preferred binding agents haveglass transition temperatures (T_(g)) from about -15° C. to about 150°C., preferably from about 35° C. to about 110° C., and most preferablyabout 50° C. The most preferred binding agents are chosen based upontheir potential strong chemical interactions with the surface to beprinted. Specifically envisioned as factors to be considered asproviding the potential for strong chemical interactions are thelikelihood of formation of bonds such as ionic or covalent bonds,donor-acceptor bonds, as well as secondary bonds such as hydrogen bondsand van der Waals bonds between the binding agent and the surface to beprinted. In evaluating the potential, the relevant bond energies may beobtained from textbooks such as Adhesion and Adhesives: Science andTechnology by A. J. Kinloch; 1987, University Press Cambridge, GreatBritain.

Additionally, the most preferred binding agents can be laminated, whenincorporated in a dry toner powder, at temperatures of from about 50° C.to about 240° C., preferably at temperatures of from about 120° C. toabout 200° C. For example, the well known REFLECTO-LITE brandretroreflective sheeting available from the Minnesota Mining andManufacturing Company of St. Paul, Minn., has a polyvinyl butyralsurface and therefore compatible binding agents, which cause dry tonerpowders to laminate at temperatures from about 50° C. to about 240° C.,may be fused during lamination of an ethylene acrylic acid (EAA)copolymer protective film to the retroreflective sheeting. Laminatingtemperatures refer to those measurable at the surface of rollers 132 and240 in FIGS. 2 and 3 respectively. Temperatures at surfaces such as 102in FIG. 2 or 202 in FIG. 3 may be lower than the laminating temperaturesmentioned here. Most preferred are binding agents which may be used attemperatures of about 150° C. Preferred binding agents are alsoresistant to ultraviolet (UV) light degradation and are adhesive to thesurface upon which the toner is printed.

Suitable charge carriers may be positive charge control agents designedfor use as additives in dry toner formulations such as, for example,copolymers of butyl and methyl methacrylate (such as TRIBLOX PC-100brand acrylic polymer (available from E. I. DuPont de Nemours Company)).Polyesters and vinyl resins may also be used as charge carriers. Apreferred acrylic copolymer charge carrier has the followingcharacteristics: molecular weight of 2000 to 5000; glass transitiontemperature (Tg) of 53° C. to 59° C., onset at about 46° C., nitrogencontent of about 1% as measured by NMR. Preferred charge carriers arealso relatively light transmissive or transparent materials, and areresistant to UV light degradation. For a black toner, a transparentcharge carrier is not essential. For example, an azine dye (NigrosineSolvent Black 7, CI#50415:1) available from the Orient Chemical Company,port Newark, N.J., may be used as a charge carrier for such a toner. Themost preferred charge carriers are acrylic polymers (i.e. alkylacrylates or alkyl methacrylates) having amine functionality (i.e.functional groups including amine nitrogen or quaternary ammoniumnitrogen).

Suitable colorants may be pigments such as Pigment Red 179 or 224available from the Harmon-Mobay Chemical Company; Pigment Yellow 110 orPigment Violet 37 available from the Ciba-Geigy Company; Pigment Green 7or 36 available from the Sun Chemical Company; Pigment Blue 15;1 or Blue15;6 available from BASF; and Regal 500R carbon black available from theCabot Corporation. Suitable colorants may also be dyes such as AmaplastYellow available from the Color-Chem International Corporation or LATYLBrilliant Blue BGA available from the DuPont Company. Generally,pigments or dyes should be resistant to environmental pollutant chemicaldegradation and UV light degradation. Preferably, pigments are dispersedin a dispersing resin, for example Red 229 dispersed in Vinylite VAGHresin in a 1:1 weight ratio. Such dispersion helps to maintain the smallpigment particle size that is desired for obtaining a light transmittantimage.

The fused toner image on retroreflective signs is preferably lighttransmissive for all colors except black. That is at least 10% of lightentering the image area passes through the toner, except in the case ofcarbon black. In the case, however, of black images resulting from theuse of carbon black, the fused toner image is preferably opaque. Thatis, none of the light entering the black image area passes through thetoner.

Suitable dry powder toners may be prepared by combining from about 64%by weight to about 98% by weight binding agent with about 1% by weightto about 20% by weight charge carrier agent and with about 1% by weightto about 16% by weight colorant; preferably combining from about 76% byweight to about 92% by weight binding agent with about 2% by weight toabout 12% by weight charge carrier agent and with about 6% by weight toabout 12% by weight colorant; and most preferably combining about 88% byweight binding agent with about 4% by weight charge carrier agent andabout 8% by weight colorant.

The binding agent, charge carrier agent and colorant may be mechanicallymixed (and the binding agent as well as the charge carrier melted) usinga twin screw extruder such as a variable speed twin screw extruder, forexample a Baker Perkins gear drive model having a Haake rheocord torquerheometer. Preferably, the twin screw extruder generates a temperatureof approximately 150° C. to approximately 225° C. during extrusion. Theextruded product may be hammer milled and then jet milled to generate amixture having particle sizes ranging from about 5 to about 100micrometers, preferably from about 5 to about 50 micrometers and mostpreferably from about 5 to about 20 micrometers. A suitable jet mill isa NPA Supersonic Jetmill model PJM IDS-2 available from the NipponPneumatic Manufacturing Company. The resulting material may be used inthe toner hopper of a laser type printer.

Suitable surfaces of sign components to be printed may be made frommaterials including polymers selected from the group consisting ofpolyalkylacrylates, polyalkylmethacrylates, polyesters, vinyl polymers,polyurethanes, cellulose esters, fluoropolymers, polycarbonates,polyolefins, ionomeric copolymers and copolymers of ethylene orpropylene with acrylic acid, methacrylic acid, or vinyl acetate.Suitable retroreflective sheetings include SCOTCH-LITE brand HIGHINTENSITY retroreflective sheeting and REFLECTO-LITE brandretroreflective sheeting. The surface layers may be made ofpolyalkylacrylates or polyalkylmethacrylates (especially polymethylmethacrylate (PMMA)), polyesters, vinyl polymers and polyvinyl acetalssuch as, for example, polyvinyl butryals. The SCOTCH-LITE brand andREFLECTO-LITE brand retroreflective sheetings are available from theMinnesota Mining and Manufacturing Company of St. Paul, Minn.

A wide range of electrophotographic printers may be used to practice thepresent invention. One suitable printer is a 3M brand MultifunctionPrinter Model 1800 available from the Minnesota Mining and ManufacturingCompany of St. Paul, Minn. The Model 1800 printer was originallydesigned for automatic paper-feed, but may be operated on continuouswebs with modifications which are within the skill of the art. The drypowder toner of the present invention is substituted for the tonerusually used with the printer. The Model 1800 printer is a dual-modeprinter. The printer is capable of printing from 35 mm aperture cards ormicrofilm. The printer also accepts digital information from a hostcomputer (such as a Sun Microsystems Computer) in the form of rasterfiles. Another suitable printer is a 3M brand Model 679 LBQ LASERPRINTER available from the Minnesota Mining and Manufacturing Company ofSt. Paul, Minn. Preferably, such a printer is used in conjunction with a3M brand Model 1811 CONTROLLER, also available from the Minnesota Miningand Manufacturing Company. Both of these printers are capable of 200dots per inch (dpi) (i.e. 79 dots per centimeter or 3.95 line pairs permillimeter) horizontal and vertical resolution and accept raster datafiles either from a raster-based host system (such as a Sun MicrosystemsComputer) or vector-based host system through a vector-to-rasterconverter.

DESCRIPTION OF COMPUTER PROGRAM

A preferred computer program for defining license plate images which iswritten in the "C" computer language for use on a Sun MicrosystemsComputer is included on microfiche with this description. Standardcomputer programs for defining an image to be printed, in the form ofraster files, are well known. However, many of these programs tend tosuffer from a lack of speed in defining an image and/or tend to produceimages with unacceptably "rough" edges when enlarged to sizes typicallyemployed for an alpha numeric image on a license plate (i.e. about 6.0cm in height). For example, Artisan™, a graphics printing programavailable from Media Logic, Inc. of Santa Monica, Calif. and SunDraw™, agraphics printing program available from Sun Microsystems, Inc. ofMountain View, Calif., each provide one bit raster character fileshaving only about 20% of the resolution of the program of thisinvention.

The preferred computer program is capable of utilizing the bestresolution of the printer, that is 200 dots per inch (i.e. about 7.9dots per millimeter or 3.95 dots per millimeter). The program alsoprovides a number of "prompting screens" to a video monitor to enable anoperator to compose and review an image for alpha numeric identificationon a license plate. The images are reviewed in reduced or downsized formto enable the image for an entire plate to be reviewed on a videomonitor.

The computer program of the present invention may be generallyunderstood by reference to the overview of FIGS. 5 and 6. In thefollowing description, two forms of raster files are mentioned: rawraster files and Sun raster files. By "raw raster files" is meant rasterfiles having a specific identifying header for recognition andprocessing compatibility within the program of this invention. Thoseskilled in the art will recognize that many alternative identifyingheader types could be used to render raster file data structuresinternally consistent within a program.

FIG. 5 shows an overall data flow pattern associated with program. Thedata initially supplied to the computer operating the program may beprovided either as an eye readable image, such as an image on paperwhich may be optically scanned and entered at the scanner interface oralternatively, the image may be programmatically developed, such as thealpha numeric characters generated for license plates.

From the scanner interface, the scan function acts on the input imageand converts it into an 8-bit Sun raster file which includes grey scaleinformation. The contrast function converts the 8-bit raster file into a1-bit Sun raster file which is in black and white form.

The data for defining an image may also be provided by using thecharacter function. Data generated by the character function is storedin a character library file. The makestring function is used to combinea plurality of files of individual characters from the characterlibrary, then act upon the combined data and converts it to a 1-bit Sunraster file. Once an image is available as a 1-bit Sun raster fileformat, either the merge function and/or the scale function may be usedto enhance or modify the final image. A 1-bit Sun raster file may beconverted by the print function into a 1-bit raw raster file and thensent to the printer, via a Versatec printer interface, for conversionfrom raster form into a laser written latent image on a reusable drumsurface. As explained earlier, portions of dry toner powder are acceptedby the latent image portions of the reusable surface and subsequentlytransferred to the polymeric surface to be printed.

In the data flow diagram of FIG. 5, the large outside circle representsall of the program or software of this invention within the computer.The four smaller circles represents classes of files, such as 8-bit Sunraster files, compressed 1-bit Sun raster files, 1-bit Sun raster files(uncompressed) and 1-bit raw raster files. Within the class of 1-bit Sunraster files, several types may occur. For example, a 1-bit Sun rasterfile might be a file resulting from a scanned image, a programmaticallydeveloped image, such as a single alpha numeric character, a fileresulting from operation of the merge function on a pre-existing 1-bitSun raster file, or a file resulting from operation of the scalefunction on a pre-existing 1-bit Sun raster file. Files may be reviewedthrough the printing process or by well known screen preview programs.The 1-bit Sun raster files have a 36 byte header which indicate the datalength of the file, the raster line length and the height, and thenumber of lines per image. A 1-bit raw raster file by comparison, has tobe predefined for the printer. The print function requires files with aheader including the definition of the line width, typically pre-definedas 400 bytes per line.

As shown in FIG. 6, a process control flow chart shows the major logicalflow of the program through all the functions. Beginning with the scanfunction, an image file is converted from a grey scale to a 1-bit Sunraster file using the contrast function. A user may review and confirmthat an image file corresponds to the desired image. If not, the usermay edit that image file or rescan the image. A user may repeat thissequence until the image is acceptable. An acceptable image is purelysubjective to the user, however, for a typical license plate, anacceptable image will typically be recognized as large, solid printedalpha numeric regions on an unprinted background. Further, the edges ofthe alpha numeric image will be well defined, smooth lines or curves.Once an acceptable image file is present, the user proceeds to the nextdecision box.

Alternatively, a user may programmatically generate character filesusing the make character function. A collection of character files isstored in compressed form in a library. A different library may beformed for each complete set of images. From the compressed characterfiles in a library, the makestring function combines a particularselected set of files to form a string of characters. For example, if adesired image string were "ABC"; the makestring function would firstobtain the file for "A", second, the function would obtain the file for"B", third, the function would obtain the file for "C"; fourth, thefunction would append the files together; and fifth, the function wouldstore the appended file as a 1-bit Sun raster file.

Next, a user may check the image for acceptable size. If unacceptable,the user can use the scale function to increase the size or decrease thesize of that image. For example, if an image corresponding to theStatute of Liberty had been scanned in, the image size might beacceptable in shape but unacceptably small, for example only half thedesired size. The user could double the image size using the scalingfunction. Once the scaling function is used, a new 1-bit Sun raster fileis formed.

The next step is to combine a character string and another image usingthe merge function. For example, the Statute of Liberty file might becombined with a character string file for a vehicle identificationnumber, the two initial files and the final file being 1-bit Sun rasterfiles. Additional files may be subsequently added one at a time or threeor four images can be combined in one operation.

Once a desired combined image file is formed, the file may be printed.Any 1-bit Sun raster file may be accepted by the print function and sentto a Versatec printer interface. Those skilled in the art will recognizethat raw raster files could alternatively be sent to other types ofprinter interfaces having the capability of accepting raw raster dataand driving raster printers. The print function may also take a numberof print files and sequentially send them to the printer.

A more detailed description of the particular functions of the preferredprogram, with reference to FIGS. 7 through 14, follows.

As shown in the flow chart of FIG. 7, the make character function of theprogram allows a user to programmatically prepare files for specificimages. For example, in the case of vehicle identification numbers forlicense plates, a user may wish to prepare a set of alpha numericcharacters.

A graphical user interface is displayed upon the computer screen toassist and prompt the user for this and other functions. The user firstselects or accepts an appropriate character size input. The makecharacter function of the program accepts the character size input andnext allows programming of a group of standard raster lines that arerepeated as portions of characters within a set of characters. The makecharacter function also designates a "library" or directory for storageof the character files being prepared. Next, the program proceeds toprompt for the next character to be prepared. For a set of alpha numericcharacters, the process is repeated 36 times, once for each numeral andletter. For each character, each raster line must be checked. The nextline count allows the progressive advancing to the next raster line ofthe character file. For example, a 3 inch (7.6 cm) high character fileat a resolution of 200 dots per inch, has about 600 raster lines,corresponding to about 600 horizontal lines.

If a particular raster line corresponds to a portion of the characterthat may be present in a repetitive or standard format, then thatstandard format is used. For example, a letter "I" has two cross orhorizontal bars connected by an upright or vertical bar. In the regionof the upright bar, each raster line includes a portion or line segmentof the upright bar. Thus, each raster line going through the upright baruses the standard pregenerated raster line segment to reduce theprogramming effort required for the character file "I". Similarly,standard raster line segments may be prepared for the two cross bars.Next, the user decides whether any more raster lines are needed toprepare the file. For example, if line number 300 has been written andthe same line will be repeated until line 600, we go get the next line.

An alternative logic route is followed when a standard line is notappropriate. For example, in the case of the curves in the letter "C".The program calculates where the printed portion would appear for eachraster line, depending upon the size of the characters to be printed.

Typically, character files are not long, although the more complex alphanumeric characters i.e. "S", "2" and "5" tend to be relatively large.Specific program steps or lines are provided in the accompanyingmicrofiche.

One of the final operations of the make character function is tocompress the file. Compression of files serves to reduce the totalamount of data in the file and more efficiently uses memory as well asspeeding data retrieval in later functions.

The logic of the scan function is shown in FIG. 8. Again the scanfunction causes the display of a user interface screen to prompt andassist the user. The scan function first accepts a set of scannerparameters regarding the size of the image. The scan function verifiesthat the selected parameters are such that the scanner can supply thenumber of lines corresponding to the lines specified by the parameters.Parameters exceeding the accepted boundaries are rejected and the userprompted to supply appropriate parameters. Next, a communication line tothe scanner is opened and an output file opened to accept the data. Forexample, a Howtec scanner is capable of the following resolutionpossibilities: 75 dots per inch, 100 dots per inch, 150 dots per inch,200 dots per inch and 300 dots per inch.

The scanner then provides information on a line by line basiscorresponding to the eye readable image being scanned. The information,on a line by line basis is written to the output file. The resultingscan data is in 8-bit format, in order to include grey scale informationfor each pixel or dot. If an image was scanned at a resolution of 300dots per inch in 10 inches, that would entail 3,000 lines and 3,000repetitions of the logic loop. Finally, the scanner device and theoutput file would be closed.

As shown in FIG. 9, the contrast function is used to convert the greyscale 8-bit image information from the scanner to a black and white(print/no print) system more suitable for a reflective sign. A userinterface screen from the contrast function prompts for a file name. Ifthe file exists, the program retrieves it and proceeds. The functionfirst assists the user in selecting the best contrast point, i.e. aparticular number between 0 and 255 which serves as the best arbitrarydivision between grey scale values which will be considered black andgrey scale values which will be considered white. Generally, the bestcontrast point is found from the distribution curve of frequency ofoccurrences plotted against grey scale value. On such a distributioncurve, the best contrast point is a minimum (preferably the deepestminimum) located between a pair of maximums (as opposed to a minimum atone end of the grey scale.)

After selecting the best contrast point, the file is converted bychanging the data from an 8-bit file header to 1-bit file header.Effectively, the conversion divides the total file length by 8 andchanges the grey scale tones to black or white. Each raster line is readuntil we find the end of file. If 600 raster lines are used, the processis repeated 600 times. Within the data, each byte representing greyscale information greater than the contrast point is set to 0. Bytesless than the contrast point are set to 1. (Note that the 1-bit rasterformat has 0 equal to white and an 8-bit raster format has 0 equal toblack.) Once the end of each raster line is reached, the next rasterline is started until all the data has been processed, then the file isclosed.

As shown in FIG. 10, the makestring function initially prompts andaccepts user input consisting of a string of characters and a charactertype, corresponding to a predefined library. For example, for a 7 digitlicense plate for the U.S. displaying six characters and one blank, thepreferred characters are about 3 inches high by about 1.25 inches wide(i.e. 7.6 cm×3.2 cm).

The file for each selected character is retrieved and uncompressed toprovide a 1-bit raster format. The parameters of the output file arecomputed next. This entails adding the widths of all the character filestogether and then combining the width times the height of the character.For example, for a license plate having six letters each of image size 3inches (7.6 cm) high by 1.25 inches (3.2 cm) wide the file mustaccommodate about 900,000 dots (i.e. 1.25 inches/letter×6 letters×200dots per inch)×(3 inches/letter×200 lines/inch). The files are combinedby first reading a line from each file. Each of these lines should bethe same number of lines down from the top of the image. The lines arenext appended to form a single line. The process eventually results in aset of 600 output lines. The output lines are then written to an outputfile. Finally, the output file is compressed and sent to the library.

As shown in FIGS. 11 and 12, the scale function is best explained as atwo part function. In the first part, shown in FIG. 11, the verticaldimension of the image is expanded or contracted by adding orsubtracting raster lines. In the second part, the horizontal dimensionof the image is expanded or contracted by adding or subtracting datafrom each raster line.

As shown in FIG. 11, a user first instructs or inputs the file name andscale value. The scale value may be any value from 0 to 2.0 inincrements of one-tenths. The scale value of 2.0 means that the imagewill be doubled on in both width and height and therefore the resultingimage will be four times the area of the initial image. Conversely if ascale factor of 0.5 is chosen the resulting image will be half as highand half as wide and the area will be one-quarter of the original. Forclarity of explanation, the process will be explained for a scale factorof 2.0 (i.e. a doubling of image height and width.)

Next, the initial file is read entirely into the buffer. The initialfile is treated as a two dimensional array of lines and height. Thealgorithm begins by finding the line segments for the first line. Thisfirst line is temporarily named "y" or "previous line". The next line isfound and temporarily named "x" or "current line". The two lines areevaluated in order to calculate a line which will be inserted betweenthe previous and current lines and thereby begin to double the imageheight. Beginning points of line segments, (i.e. portions which will beprinted) are averaged to determine a beginning line segment point forthe new line. Similarly, ending points are averaged to determine anending point for the new line segment. For example, if a beginning pointof line y is at raster No. 232, and the beginning point of line x is atraster No. 234, then the line segment in the new line begins at rasterdot 233. If the end point of line y is at 555 and the end point of linex is at 575, then the new line segment end point is at 565. Next, thepoints between the beginning and the end of the new line segment arefilled with "ones", such that those points will be printed as a blackline segment. For some lines there may be multiple line segments,however all of the line segments in lines x and y that match or arepartially overlapping are treated in the above manner.

The result is a newly calculated line inserted between the line y, whichis on the top, and line x, on the bottom, and an image having increasedheight. To continue, a newer line must be calculated for insertionbetween the current line and the next successive line of the originalimage. For scale factors between 1.0 and 2.0, proportionately fewerinsertions of newly calculated lines are made. For scale factors lessthan 1.0, a proportionate number of lines are deleted and no new linesneed be calculated.

In the second part of the scale function, as shown in FIG. 12, thelength of the line segments to print will be increased or decreased.Each pixel or dot is treated as a member of a vertical column. Verticalcolumns are calculated and inserted to expand the image or alternativelydeleted to reduce the image based upon the scale factors used in thefirst part of the scale function.

The completed image file resulting from the scale function is in 1-bitSun raster format and is written to a new file. The new 1-bit Sun rasterfile can be merged, scaled or printed.

As shown in FIG. 13, the merge function allows a user to combine aplurality of image files into a single file. The user begins byidentifying the files desired to be merged together and entering thefile names. Next, the function computes the dimensions for the filewhich will be output based upon the dimensional parameters of the filesto be merged. If an unprinted border is desired, the border values areadded to the file dimensions and the top border lines written to the newfile. Next, the function determines whether there are more lines tocombine. Subsequently, a raster line of each file is combined into asingle new raster line and written to the new file. Finally, a bottomborder may be added.

The print function as shown in FIG. 14, begins by accepting the filenames of the files to be printed. If the file does not exist, the useris notified and requested to enter another file name. This function isdesigned to sequentially print multiple files and produce prompts foradditional files. When all the files to be printed have been identified,the function proceeds to open an input file and to open a print file,specifically, a 1-bit raw raster file. (A 1-bit raw raster file is shownin the data flow diagram of FIG. 5 as a circle.) Next, an input linefrom the input file is read. The input line is padded or truncated, ifnecessary, to assure that the line will contain exactly 400 bytes ofinformation. Next, the input file and output 1-bit raw raster file areclosed. Immediately following that, the 1-bit raw raster print file isreopened as an input file and the printer device (a Versatec printerinterface) is opened as output. A block of data is read from the inputfile. The block may be of any size, however, it is preferred that theentire file is used as a single unit. Once the data has been read intothe buffer, the data is written to the printer. At the end of the file,an end of file command is sent to the printer device and the next fileto print is found.

In summary, the computer program of the present invention includes anumber of program steps which, in combination, perform the majorfunctions of the program. Specifically, the program includes: a functionfor making a character which may be used as an image or a portion of animage; a function for scanning in eye readable images; a function foradjusting contrast from grey scale to black and white; a function foradjusting scale or size of the image definition; a function forassembling the individual characters into a string; a function formerging an image definition with a second preferably repetitive image;and a function for sending the image definition to a printer.

EXAMPLE 1

A mixture was prepared of 88% Acryloid B-66 binder resin (Rohm & HaasCompany), 4% TRIBLOX PC-100 charge carrier (DuPont Company) and 8%carbon black (Regal 500R from Cabot Corporation). The components weremixed in a Baker Perkins gear drive variable speed twin screw extruderwith a Haake rheocord torque rheometer and extruded as a mixture at atemperature range between 150° C. to 225° C. The extruded mixture washammer milled, and subsequently jet milled in a NPK supersonic jetmillmodel PJM IDS-2 from Nippon Pneumatic Manufacturing Company. The jetmilled sample was then classified to collect material having a particlesize range from 5 to 20 micrometers. This material was placed in thetoner hopper of a 3M brand MODEL 1800 MULTIFUNCTION PRINTER. A computerprogram (appended) digitally defining alphanumeric images 7.0 cm inheight as raster files was used to print upon REFLECTO-LITEretroreflective sheeting. The printer applied toner powder to thedefined images. Subsequent to printing the toner was fused in theprinter. The toner adhered well to the sheeting.

EXAMPLE 2

A mixture was prepared of 88% Acryloid B-66 binder resin (copolymer ofmethyl and butyl methacrylates from Rohm & Haas Company), 2.3% NigrosineSolvent Black 7, CI#50415:1 (Bontron N-01 from Orient Chemical Company)and 8% carbon black (Regal 500R from Cabot Corporation). The componentswere mixed and processed as described in example 1. After classifyingand collecting, this toner was tested using a 3M brand MODEL 1800MULTIFUNCTION PRINTER following the procedure given in example 1.

EXAMPLE 3

The retroreflective sheeting and fused image from Example 1 was firstexposed to corona treatment (see U.S. Pat. No. 4,844,976, column 9) andthen laminated to an ethylene acrylic acid (EAA) transparent cover filmat a temperature of 150° C. and a nip roll pressure of 19 kg/cm ofwidth. Both the retroreflective sheeting and the EAA were drawn past acorona treater for exposure to about 2.4 kw per meter of width topromote lamination adhesion. The alpha numeric image was sandwichedbetween the retroreflective sheeting and the transparent EAA cover film.Because the EAA film tends to lack adequate dimensional stability, apolyester carrier web was initially employed to provide dimensionalstability to the EAA film. The carrier web was recovered after passagethrough the nip. The EAA adhered well to the layers below. The printedalpha numeric image was apparent through the transparent cover film. Thelaminate, including the sandwiched image, was applied to an aluminumlicense plate blank to form a completed license plate.

EXAMPLE 4

An embossed aluminum licence plate blank including a REFLECTO-LITEretroreflective sheeting layer was printed with the dry toner powder ofExample 1 as follows: a portion of the dry toner powder was spread on asurface and a hand-held hard rubber roller was rolled over the toner toload the surface of the roller with toner. Next the roller was rolledover the raised portions of the embossed plate which had been slightlywarmed. The powder transferred to the raised portions, adhering to theraised portions of the polyvinyl butyral surface. Next, the plate washeated to fuse the powder. The black printed image was clearly visibleon the lighter colored retroreflective sheeting and corresponded to theraised image.

The combination of the reflective sheeting surfaces listed above withthe solid toners described is unique, as is the use of anelectrophotographic printing process to make a sign such as a licenseplate. The toners described are solid and capable of working in theelectrophotographic process, adhering well to the reflective sheetingsurface. The inventive process decreases air pollution from solventvapors which are released from liquid inks and eliminates the investmentin drying ovens and solvent recovery equipment that are associated withliquid ink processes.

Although the present invention has been described with reference to thepreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A reflective sign comprising a retroreflectivesheet:A. having an image bearing surface, intended to be seen by anobserver, which comprises a polymer selected from the group consistingof polyalkylacrylates, polyalkylmethacrylates, polyesters, vinylpolymers, polyurethanes, cellulose esters, fluoropolymers,polycarbonates, polyolefins, polyvinyl acetals, ionomeric copolymers andcopolymers of ethylene or propylene with acrylic acid, methacrylic acid,or vinyl acetate; B. said image bearing surface having printed thereonan image derived from a solid toner comprising:(1) a colorant; (2) atransparent polymeric binding agent, which adheres to said image bearingsurface, selected from the group consisting of alkyl substituted acrylicand methacrylate polymers with alkyl groups having 1-9 carbon atoms,polyvinyl acetals, polyolefins, polyesters and vinyl resins; and (3) acharge carrier selected from the group consisting of:acrylic polymerswith functional groups having at least an amine nitrogen or quaternaryammonium nitrogen; methacrylic polymers with functional groups having atleast an amine nitrogen or quaternary ammonium nitrogen; and azine dyes.2. The sign of claim 1, wherein the printed image is light transmissive.3. The sign of claim 1 wherein the binding agent consists of a copolymerof methyl methacrylate and butyl methacrylate.
 4. The sign of claim 1which further comprises:a supporting substrate to which the reflectivesheet is adhered.
 5. The sign of claim 4 wherein the supportingsubstrate comprises a material selected from the group consisting ofaluminum, steel, and polymeric materials.
 6. The sign of claim 1 furthercomprising: a light transmitting protective top layer covering thereflective sheet layer and the fused toner so as to place the imagebetween the reflective sheet layer and the transparent top layer.
 7. Thesign of claim 1 and further comprising: an embossed area on which theimage derived from solid toner has been printed.